Electrical discharge state detecting device for electrical discharge machining machine

ABSTRACT

An electrical discharge state detecting device for an electrical discharge machining machine which detects an electrical discharge state during an electrical discharge machining operation. The detecting device includes a high-pass filter for detecting a high-frequency component superimposed on an electrical discharge voltage or an electrical discharge current at a machining clearance between an electrode and a workpiece, a rectifying circuit for outputting a rectified component of the high-frequency component, a first integration circuit for integrating the rectified component, a reference voltage circuit, a second integrating circuit for integrating the reference voltage, a comparator for comparing the two integrated values, an electrical discharge generation detecting circuit for controlling starting and ending of the integrating circuits, a logic circuit, and a delay circuit and reset circuits.

This is a divisional of application Ser. No. 09/071,942 filed May 5,1998, now U.S. Pat. No. 6,208,150, which is a divisional of U.S. Pat.No. 5,751,155 issued May 12, 1998 (U.S. application Ser. No. 08/510,849filed Aug. 3, 1995), the disclosure of which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to an electrical discharge state detectingdevice for an electrical discharge machining machine which detects anelectrical discharge state during an electrical discharge machiningoperation.

BACKGROUND OF THE INVENTION

Conventionally, it is known that an electrical discharge state in anelectrical discharge machining in an electrical discharge machine can bejudged by detecting the magnitude of a high-frequency component of theelectrical discharge voltage waveform. This electrical discharge voltagewaveform is a quite complex waveform including a high-frequencycomponent. Accordingly, it is quite important to provide a technique inwhich only a characteristic waveform component is detected from theelectrical discharge voltage waveform without fail and at high speed.

Japanese Laid-Open Patent Publication No. 5-293714 discloses anelectrical discharge state detecting device for an electrical dischargemachine. Referring to FIG. 11, illustrating a circuit of substantiallythe same constitution as that of this reference, the operation of thisdevice will be described hereunder.

In FIG. 11, reference numeral 2 denotes an electrode of an electricaldischarge machine, reference numeral 3 denotes a workpiece, and amachining clearance is formed between the electrode 2 and the workpiece3. Reference numeral 1 denotes a machining power source of theelectrical discharge machining machine. An electrical discharge voltagein the form of a pulse is supplied from the machining power source 1 tothe machining clearance between the electrode 2 and the workpiece 3.Reference numeral 4 denotes a high-pass filter for use in detecting ahigh-frequency component of the electrical discharge voltage, referencenumeral 5 denotes a rectifying circuit for rectifying the high-frequencycomponent from the high-pass filter 4, and an output signal vrec isoutputted from the rectifying circuit 5. In addition, reference numeral6 denotes an electrical discharge generation detecting circuit fordetecting generation of the electrical discharge in the machiningclearance between the electrode 2 and the workpiece 3. The electricaldischarge generation detecting circuit 6 is composed of an electricaldischarge voltage detecting circuit 60 for detecting the electricaldischarge voltage at the machining clearance between the electrode 2 andthe workpiece 3 and of an electrical discharge current detecting circuit61 for detecting an electrical discharge current at the machiningclearance between the electrode 2 and the workpiece 3.

An output signal 60 s of the electrical discharge voltage detectingcircuit 60 and an output signal 61 s of the electrical discharge currentdetecting circuit 61, in the electrical discharge generation detectingcircuit 6, are inputted to a logic circuit 62. Reference numeral 7denotes a delay circuit. The delay circuit 7 is composed of a timeconstant circuit 70 for measuring a time constant tH of the high-passfilter 4 and of a logic circuit 72. An output signal 63 from the logiccircuit 62 is inputted to the time constant circuit 70 and the logiccircuit 72 in the delay circuit 7. An output signal 71 from the timeconstant circuit 70 is inputted to the logic circuit 72. Referencenumeral 8 denotes an integrating circuit. The integrating circuit 8 iscomposed of an operational amplifier 80, a capacitor C1 connectedbetween the inverting (−) input terminal and the output terminal of theoperational amplifier 80, and a resistor R1 connected in series betweenthe output terminal of the rectifying circuit 5 and the inverting (−)input terminal of the operational amplifier 80. In addition,non-inverting (+) input terminal of the operational amplifier 80 isconnected to the ground.

Reference numeral 9 denotes a reset circuit. The reset circuit 9 iscomprised of a transistor of which collector-emitter terminals areconnected between both terminals of the capacitor C1. An output signal73 from the logic circuit 72 of the delay circuit 7 is inputted to thereset circuit 9. Then, reference numeral 10 denotes a comparator. Anintegrated output value Vint as the output signal from the operationalamplifier 80 of the integrating circuit 8 is inputted to the inverting(−) input terminal of the comparator 10, and a reference voltage Vref isinputted to the non-inverting (+) input terminal of the comparatorcircuit 10.

FIG. 12 shows input and output signal waveforms at main parts in FIG.11. Reference character A in FIG. 12 indicates an electrical dischargevoltage waveform at the machining clearance between the electrode 2 andthe workpiece 3. Reference character B in FIG. 12 indicates an outputsignal waveform of the high-pass filter 4. Reference character I in FIG.12 shows an output signal waveform in the logic circuit 72. Referencecharacter F in FIG. 12 shows an integrated output signal waveform of theintegrating circuit 8.

The operation of this arrangement will be described referring to FIGS.11 and 12.

In FIGS. 11 and 12, reference numeral 20 denotes an electrical dischargevoltage waveform at the machining clearance between the electrode 2 andthe workpiece 3, wherein Ton denotes an electrical discharge pulse widthand Toff denotes a rest time. When an electrical discharge is generatedafter applying a voltage to the machining clearance between theelectrode 2 and the workpiece 3, both the output signals from theelectrical discharge voltage detecting circuit 60 and the electricaldischarge current detecting circuit 61 become H (high) levels. Theseoutput signals are inputted to the logic circuit 62. In the logiccircuit 62, when all these input signals become H levels, i.e., when anelectrical discharge is generated at the machining clearance between theelectrode 2 and the workpiece 3, an L (low) level is outputted. Such atime is defined as an electrical discharge detecting time t1. t2 denotesa time (t2=t1+tH) after the time constant tH of the high-pass filter 4from the electrical discharge detecting time t1. Reference numeral 21denotes a high-frequency component of the electrical discharge voltage.Reference numeral 22 denotes a disturbance waveform caused by atransient characteristic of the high-pass filter 4.

In the time constant circuit 70, the H level is outputted for the timeperiod tH from the fall time of the output signal 63 of the logiccircuit 62. The output signal 63 of the logic circuit 62 and the outputsignal 71 of the time constant circuit 70 are inputted to the logiccircuit 72, and then the output signal 73 indicated at the code I inFIG. 12 is outputted. The rise time of the output signal 73 is definedas t2 at I in FIG. 12. The reset circuit 9 resets the integratingcircuit 8 for a period when the output signal 73 of the logic circuit 72is the H level. That is, the output signal vrec from the rectifyingcircuit 5 is integrated at the integrating circuit 8 only for a periodwhen the output signal 73 of the logic circuit 72 is the L level. In thecomparator 10, the reference voltage Vref and an integration output Vintindicated by F in FIG. 12 are compared with each other. When theintegration output Vint is higher than the reference voltage Vref at theend of the electrical discharge pulse width Ton, it judged to be anormal electrical discharge pulse. Otherwise, it is judged to be anabnormal electrical discharge pulse such as an arc electrical dischargepulse.

However, the aforesaid electrical discharge machining machine has somedisadvantages as described below.

Referring to FIGS. 13a and 13 b, a first disadvantage will be described.

FIGS. 13a and 13 b are timing charts respectively showing a relationbetween an electrical discharge voltage waveform 20 and an integrationoutput value Vint in the case that the same machining current value isselected. FIG. 13a shows a case in which the electrical discharge pulsewidth is a large one Ton1, and FIG. 13b shows another case in which theelectrical discharge pulse width is a small one Ton2.

The integrated output value Vint from the integrating circuit 8 can beexpressed by the following equation (1).

Vint=vrec×Ton/(R1×C1)   (1)

where, vrec denotes an output signal from the rectifying circuit 5, Tondenotes an electrical discharge pulse width, R1 denotes a resistancevalue for determining an integration gain of the integrating circuit 8,and C1 denotes an electrostatic capacitance value for determining theintegrating gain of the integrating circuit 8. It is known that amagnitude of the high-frequency component of the electrical dischargevoltage depends on a magnitude of the machining current. However, asapparent from the equation (1), even if the same machining current valueis selected as the machining condition, the integration output valueVint is proportional to the electrical discharge pulse width Ton.

As shown by the integration output signal waveforms F in FIGS. 13a and13 b, it is necessary to change and set the reference value Vref inaccordance with the electrical discharge pulse width Ton, which is setas a machining condition. The electrical discharge pulse width Ton isset, as the machining condition, to have a wide value ranging from aminimum value of about 2 sec to a maximum value of about 4096 sec. Then,as expressed by the equation (1), since the integration output valueVint is proportional to the electrical discharge pulse width Ton, thereference voltage Vref is also outputted, employing a data table shownin FIG. 14, corresponding to the electrical discharge pulse width Ton.Thus, a fine setting is not provided so that Vref11 is outputted as areference value in respect to a electrical discharge pulse width ofabout 1025 to 2048 sec, for example.

In addition, it is possible not to use the electrical discharge pulsewidth but to always use Ton2, for a time to be compared with thereference value Vref, in case the electrical discharge pulse width issmall. However, if the electrical discharge pulse width is large, an S/Nratio of the integrated output value Vint is decreased and thatdetecting accuracy is lowered.

Then, referring to FIGS. 15, 16 and 17, a second disadvantage will bedescribed. FIG. 15 is a circuit diagram of the machining power sourcedescribed in Japanese Utility Model Publication No. 57-33949. Referencecharacter B1 denotes a DC power source, B2 denotes an auxiliary powersource, S1 denotes a first switch, S2 denotes a second switch, D1denotes a first diode, D2 denotes a second diode, R2 denotes a currentdetecting resistor, C2 denotes a capacitor, L1 denotes a reactor,reference numeral 400 denotes a pulse generator, and reference numeral300 denotes a control circuit for the first switch S1.

FIG. 16 shows input/output signal waveforms at the main parts in FIG.15. Numerals 1 and 0 of the first switch S1 and the second switch S2denote ON/OFF states of the switches S1 and S2, respectively, whereiniL1 denotes a current waveform flowing in the reactor L1 which isdetected by the current detecting resistor R2. The switch S2 is kept inthe ON state during a full period of the electrical discharge pulsewidth Ton. The control circuit 300 controls the switch S1 in such amanner that the output current becomes a predetermined value. As shownin FIG. 16, the switch S1 repeats ON/OFF operations for several timesduring the period of the electrical discharge pulse Ton. A large amountof electrical power is consumed in the resistor in a system which uses aresistor as a current limiting element. However, the system shown inFIGS. 15 and 16 is a current control system in which the current iscontrolled by the reactor L1 and the control circuit 300, so that it canbe said that this is a superior system in which the electrical powerconsumed in the circuit is quite low. This type of machining powersource is defined as a reactor type power source hereinbelow.

FIG. 17 shows input and output signal waveforms at the main parts whenthe reactor type power source is used in the electrical discharge statedetecting device shown in FIG. 11. Reference character A in FIG. 17indicates an electrical discharge voltage waveform, reference characterB in FIG. 17 indicates an output signal waveform of the high-pass filter4, reference character I in FIG. 17 indicates an output signal waveformof the logic circuit 72, and reference character F in FIG. 17 indicatesan output signal waveform of the integrating circuit 8. Referring to thewaveform A in FIG. 17, a spike-like voltage, which is synchronous withthe ON/OFF transitions of the switch S1, appears in the electricaldischarge voltage waveform 20 as shown by a numeral 23 in addition tothe high-frequency component 21. This spike voltage 23 is ahigh-frequency component which is generated by an operation of theswitch S1 without any relation with the electrical discharge machiningphenomenon. Erroneous detection is caused by the spike voltage 23 in theelectrical discharge state detecting device shown in FIG. 11, which isintended to detect the high-frequency component in the electricaldischarge machining phenomenon.

This erroneous detection will be described hereunder.

The component of the spike voltage 23 of the electrical dischargevoltage waveform A in FIG. 17 appears in the output signal waveform ofthe high-pass filter 4, as shown by the waveform B in FIG. 17, as thespike voltage 24. The time duration, in which the spike voltage 24appears is defined as b1 when the switch S1 is turned on, and defined asb2 when the switch S1 is turned off. On the other hand, the timeduration in which this spike voltage 24 appears depends upon themagnitude of the machining current. Reference character F in FIG. 17shows an output signal waveform of the integrating circuit 8. Itsintegrated output value increases, as indicated by a solid line, everytime the spike voltage 24 is generated. An integrated output value isshown as Vint2 when the reactor type power source is used as themachining power source, while an integrated output value is shown asVint1 when it is not used. Since the integrated output value Vint2 is asufficiently larger value than the integrated output value Vint1, it isimpossible to perform accurate detection of the high-frequency componentdue to the electrical discharge phenomenon. That is, erroneous detectionoccurs due to the electrical discharge pulse, the integrated outputvalue of the high-frequency component in the electrical dischargephenomenon is small and thus should be ordinarily be judged as anabnormal electrical discharge, but is nevertheless judged as a normalpulse.

In view of the above, the present invention is made in order to solvethese disadvantages, and it is an object of the present invention toprovide an electrical discharge state detecting device for an electricaldischarge machine which is capable of correctly detecting a normalelectrical discharge pulse in an electrical discharge state of theelectrical discharge machining.

SUMMARY OF THE INVENTION

The electrical discharge state detecting device of an electricaldischarge machine according to the invention comprises: high-frequencycomponent detecting means for detecting a high-frequency componentsuperimposed on either an electrical discharge voltage or an electricaldischarge current at a machining clearance between an electrode and aworkpiece; first integrating means for integrating, over time, themagnitude of the high-frequency component detected by the high-frequencycomponent detecting means; reference voltage output means for outputtinga reference voltage; second integrating means for integrating, overtime, the reference voltage outputted from the reference voltage outputmeans; control means for controlling the starting and ending ofintegrations by the first integrating means and the second integratingmeans; and comparing means for comparing an integrated value obtained bythe first integrating means with an integrated value obtained by thesecond integrating means, which are controlled by the controlling means.

The first integrating means may use the magnitude of a rectifiedcomponent obtained by rectifying the high-frequency component as themagnitude of the high-frequency component to be integrated over time.

The high-frequency component, which is superimposed on either theelectrical discharge voltage or the electrical discharge current at theworking clearance between the electrode and the workpiece, is detectedby the high-frequency component detecting means. The magnitude of thehigh-frequency component is obtained through time-integration in thefirst integrating means. In addition, the magnitude of the referencevoltage outputted from the reference voltage output means is subjectedto time-integration in the second integrating means. Here, the startingand ending of the integrations in the first integrating means and secondintegrating means are controlled by the controlling means. Theintegrated value obtained by the first integrating means is comparedwith the integrated value obtained by the second integrating meansthrough the comparing means. In this way, the reference voltage isintegrated by the second integrating means, and the integrated value isemployed as the comparison value for judging whether or not theelectrical discharge state of the electrical discharge machine is anormal electrical discharge pulse or an abnormal electrical dischargepulse such as an arc electrical discharge pulse. Thus, it is possible tocarry out precise setting of the reference value.

The magnitude of the high-frequency component, which is obtained throughtime-integration in the first integrating means, is the magnitude of therectified component obtained by rectifying the high-frequency component.Thus, it is possible to make the variation of the integrated valuesmaller since the magnitude of the rectified component, obtained byrectifying the high-frequency component, is integrated over time.

The invention may further be realized by an electrical discharge statedetecting device for an electrical discharge machine which comprises:high-frequency component detecting means for detecting a high-frequencycomponent superimposed on either an electrical discharge voltage or anelectrical discharge current at a machining clearance between anelectrode and a workpiece; rectifying means for outputting a rectifiedcomponent obtained by rectifying the high-frequency component detectedby the high-frequency component detecting means; first integrating meansfor integrating, over time, the magnitude of the rectified componentoutputted from the rectifying means; reference voltage output means foroutputting a reference voltage; second integrating means forintegrating, over time, the magnitude of the reference voltage outputtedfrom the reference voltage output means; integrating stopping means forstopping the integration in the first integrating means and the secondintegrating means only for a predetermined time on the basis of anoperation of an internal switching element for use in currentcontrolling of a machining power source; control means for controlling astarting and an ending of integration in the first integrating means andthe second integrating means; and a comparing means for comparing anintegrated value obtained by the first integrating means with anintegrated value obtained by the second integrating means, which arecontrolled by the controlling means.

The high-frequency component, which is superimposed on either theelectrical discharge voltage or the electrical discharge current at theworking clearance between the electrode and the workpiece, is detectedby the high-frequency component detecting means. The high-frequencycomponent is rectified by the rectifying means, and the magnitude of theoutputted rectified component is integrated over time by the firstintegrating means. In addition, the magnitude of the reference voltageoutputted from the reference voltage output means is integrated overtime by the second integrating means. The integrations in the firstintegrating means and second integrating means are stopped by theintegration stopping means only for a predetermined period of time onthe basis of an operation of the internal switching element for use incontrolling current in the machining power source. The predeterminedperiod of time is set to the time duration of the spike voltagegenerated at this time, and error factors of the integrated value areeliminated by stopping integration as above. Here, the starting andending of the first integrating means and second integrating means arecontrolled by the control means. The integrated value from the firstintegrating means is compared with the integrated value from the secondintegrating means through the comparing means. In this way, theintegrating operation is stopped only for a predetermined period of timein synchronous with an operation of the internal switching element foruse in controlling current in the machining power source, so that it ispossible to eliminate influence of disturbances and to perform accuratedetection of the electrical discharge state.

The electrical discharge state detecting device of electrical dischargemachine of the invention may also comprise: high-frequency componentdetecting means for detecting a high-frequency component superimposed oneither an electrical discharge voltage or an electrical dischargecurrent at a machining clearance between an electrode and a workpiece;rectifying means for outputting a rectified component obtained byrectifying the high-frequency component detected by the high-frequencycomponent detecting means; reference voltage output means for outputtinga reference voltage; difference output means for outputting a differencebetween the rectified component outputted from the rectifying means andthe reference voltage outputted from the reference voltage outputtingmeans; integrating means for integrating, over time, the differenceoutputted from the difference output means; integration stopping meansfor stopping integration in the integrating means only for apredetermined time on the basis of an operation of an internal switchingelement for use in current controlling of a machining power source;control means for controlling starting and ending of the integration inthe first integrating means; and comparing means for comparing anintegrated value obtained by the integrating means, which is controlledby the controlling means, with a predetermined reference value.

The high-frequency component, which is superimposed on either theelectrical discharge voltage or the electrical discharge current at themachining clearance between the electrode and the workpiece, is detectedby the high-frequency component detecting means. The high-frequencycomponent is rectified by the rectifying means, and the differencebetween the outputted rectified component and the reference voltageoutputted from the reference voltage outputting means is outputted fromthe difference voltage outputting means and is integrated over time bythe integrating means. The integration in the integrating means isstopped by the integration stopping means only for a predeterminedperiod of time on the basis of an operation of the internal switchingelement for use in controlling current in the machining power source.The predetermined period of time is set to the time duration of thespike voltage generated at this time, and error factors of theintegrated value are eliminated by stopping the integration as above.Here, the starting and stopping of the integrating means are controlledby the control means. The integrated value of the integrating means iscompared with the reference value 0 through the comparing means. In thisway, the difference between the rectified component of thehigh-frequency component and the reference voltage is integrated overtime and compared with the reference value, so that it is possible toreduce the number of integrating means and the integration stoppingmeans for stopping the integration only for a predetermined period oftime, thereby simplifying the circuit configuration.

Still further, the electrical discharge state detecting device of theinvention may comprise: high-frequency component detecting means fordetecting a high-frequency component superimposed on either anelectrical discharge voltage or an electrical discharge current at amachining clearance between an electrode and a workpiece; rectifyingmeans for outputting a rectified component obtained by rectifying thehigh-frequency component detected by the high-frequency componentdetecting means; first integrating means for integrating, over time, therectified component outputted from the rectifying means; referencevoltage output means for outputting a reference voltage; secondintegrating means for integrating, over time, the reference voltageoutputted from the reference voltage output means; integration stoppingmeans for stopping integrations in the first integrating means and thesecond integrating means only for a predetermined time on the basis ofan operation of an internal switching element for use in currentcontrolling of a machining power source; time changing means forchanging a duration of the predetermined time, for stopping theintegration in the integrating stopping means, in accordance with amagnitude of a machining current value; control means for controllingstarting and ending of the integrations in the first integrating meansand the second integrating means; and comparing means for comparing anintegrated value obtained by the first integrating means with anintegrated value obtained by the second integrating means, which arecontrolled by the controlling means.

The high-frequency component, which is superimposed on either theelectrical discharge voltage or the electrical discharge current at themachining clearance between the electrode and the workpiece, is detectedby the high-frequency component detecting means. The high-frequencycomponent is rectified by the rectifying means, and the magnitude of theoutputted rectified component is integrated over time by the firstintegrating means. The magnitude of the reference voltage outputted fromthe reference voltage output means is integrated over time by the secondintegrating means. The integrations in the first integrating means andsecond integrating means are stopped by the integration stopping meansonly for a predetermined period of time on the basis of an operation ofthe internal switching element for use in controlling current in themachining power source. The duration of the predetermined period oftime, for which the integrations are stopped by the integration stoppingmeans, is changed by the time changing means in accordance with themagnitude of the machining current value. The predetermined period oftime is properly set to the time duration of the spike voltage generatedin accordance with a magnitude of the machining current value, and errorfactors in the integrated value are eliminated by stopping theintegrations as above. Here, the starting and stopping of the firstintegrating means and second integrating means are controlled by thecontrol means. The integrated value from the first integrating means iscompared with the integrated value from the second integrating meansthrough the comparing means. In this way, a mask time limit is changedin accordance with the value of the machining current, so that it ispossible to surely eliminate the influence of disturbances and performaccurate detection of the electrical discharge state.

Still further, the invention may be practiced by an electrical dischargestate detecting device for an electrical discharge machine comprising:high-frequency component detecting means for detecting a high-frequencycomponent superimposed on either an electrical discharge voltage or anelectrical discharge current at a machining clearance between anelectrode and a workpiece; rectifying means for outputting a rectifiedcomponent obtained by rectifying the high-frequency component detectedby the high-frequency component detecting means; count means forcounting a number of continual electrical discharge pulses; firstintegrating means for integrating, over time, the magnitude of therectified component outputted from the rectifying means and adding itonly for the number of electrical discharging pulses counted by thecount means; reference voltage output means for outputting a referencevoltage; second integrating means for integrating, over time, themagnitude of the reference voltage outputted from the reference voltageoutput means and adding it only for the number of electrical dischargingpulses counted by the count means; control means for controllingstarting and ending of integration in the first integrating means andthe second integrating means; and comparing means for comparing anintegrated value obtained by the first integrating means with anintegrated value obtained by the second integrating means, which arecontrolled by said controlling means.

The high-frequency component, which is superimposed on either theelectrical discharge voltage or the electrical discharge current at themachining clearance between the electrode and the workpiece, is detectedby the high-frequency component detecting means. The high-frequencycomponent is rectified by the rectifying means. The magnitude of theoutputted rectified component is integrated over time by the firstintegrating means and added only for the number of continual electricaldischarge pulses counted by the count means. In addition, the magnitudeof the reference voltage outputted from the reference voltage outputmeans is integrated over time by the second integrating means and addedonly for the number of continual electrical discharge pulses counted bythe count means. Here, the starting and ending of the integration in thefirst integrating means and second integrating means are controlled bythe control means. The integrated value obtained by the firstintegrating means is compared with the integrated value obtained by thesecond integrating means through the comparing means. In this way, thehigh-frequency components are integrated over time for the continualelectrical discharge pulses, so that it is possible to perform accuratedetection of the electrical discharge state even if the electricaldischarge pulse width is narrow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a circuit diagram illustrating the configuration of anelectrical discharge state detecting device of an electrical dischargemachine constructed according to a first embodiment of the presentinvention.

FIG. 2 is a circuit diagram showing the construction of an electricaldischarge state detecting device for an electrical discharge machine inaccordance with a second embodiment of the present invention.

FIG. 3 is a circuit diagram showing the configuration of a mask timelimit output circuit in the electrical discharge state detecting devicefor an electrical discharge machine in accordance with the secondembodiment of the present invention.

FIG. 4 is a timing chart showing input/output signal waveforms at mainparts in FIG. 2.

FIG. 5 is a circuit diagram showing the construction of an electricaldischarge state detecting device for an electrical discharge machine inaccordance with a third embodiment of the present invention.

FIG. 6 is a circuit diagram showing the configuration of an electricaldischarge state detecting device of an electrical discharge machine inaccordance with a fourth embodiment of the present invention.

FIG. 7 is a data table showing a machining current value obtained by amask time limit output circuit, and a time width changing signalcorresponding to the mask time width, in the electrical discharge statedetecting device of an electrical discharge machine in accordance with afourth embodiment of the present invention.

FIG. 8 is a circuit diagram showing the configuration of a mask timelimit output circuit in the electrical discharge state detecting deviceof an electrical discharge machine in accordance with a fourthembodiment of the present invention.

FIG. 9 is a circuit diagram showing the configuration of an electricaldischarge state detecting device for an electrical discharge machine inaccordance with a fifth embodiment of the present invention.

FIG. 10 is a timing chart showing input/output signal waveforms at mainparts in FIG. 9.

FIG. 11 is a circuit diagram showing the configuration of a conventionalelectrical discharge state detecting device of an electrical dischargemachine.

FIG. 12 is a timing chart showing input/output signal waveforms at mainparts of FIG. 11.

FIGS. 13a and 13 b are timing charts showing the relation between anelectrical discharge voltage waveform and an integrated output value incase of selecting the same machining current value in the conventionalelectrical discharge state detecting device for an electrical dischargemachine.

FIG. 14 is a data table showing the relation between a pulse width Tonand a reference voltage Vref in the conventional electrical dischargestate detecting device for an electrical discharge machine.

FIG. 15 is a circuit diagram showing details of a machining power sourceof the conventional electrical discharge state detecting device for anelectrical discharge machine.

FIG. 16 is a timing chart showing input/output signal waveforms at mainparts in FIG. 15.

FIG. 17 is a timing chart showing input/output signal waveforms at mainparts when a reactor type power source is used in the electricaldischarge state detecting device for an electrical discharge machineshown in FIG. 11.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention is described on the basis of illustrative embodiments.

First Embodiment

FIG. 1 is a circuit diagram illustrating the configuration of anelectrical discharge state detecting device of an electrical dischargemachine constructed according to a first embodiment of the presentinvention. The same configuration as that of the aforedescribed priorart device or corresponding portions are indicated by the same referencenumerals and characters.

In FIG. 1, reference numeral 2 denotes an electrode of the electricaldischarge machine, and reference numeral 3 denotes a workpiece. Amachining clearance is formed between the electrode 2 and the workpiece3. Reference numeral 1 denotes a machining power source of theelectrical discharge machine; a pulse-like electrical discharge voltageis supplied to the machining clearance between the electrode 2 and theworkpiece 3 from the machining power source 1. Reference numeral 4denotes a high-pass filter for detecting a high-frequency component ofthe electrical discharge voltage, reference numeral 5 denotes arectifying circuit for rectifying the high-frequency component from thehigh-pass filter 4, and a rectified output signal vrec is outputted fromthe rectifying circuit 5. Reference numeral 6 denotes an electricaldischarge generation detecting circuit for the machining clearancebetween the electrode 2 and the workpiece 3. The electrical dischargegeneration detecting circuit 6 is composed of an electrical dischargevoltage detecting circuit 60 for detecting an electrical dischargevoltage at the machining clearance between the electrode 2 and theworkpiece 3 and of an electrical discharge current detecting circuit 61for detecting an electrical discharge current at the machining clearancebetween the electrode 2 and the workpiece 3.

Output signals obtained from the electrical discharge voltage detectingcircuit 60 and the electrical discharge current detecting circuit 61 ofthe electrical discharge detecting circuit 6 are inputted to a logiccircuit 62. Reference numeral 7 denotes a delay circuit, which iscomposed of a time constant circuit 70 for measuring a time constant tHof the high-pass filter 4 and of a logic circuit 72. An output signal 63from the logic circuit 62 is inputted to the time constant circuit 70and the logic circuit 72 of the delay circuit 7. The output signal 71from the time constant circuit 70 is inputted to the logic circuit 72.Reference numeral 8 denotes an integrating circuit, and the integratingcircuit 8 is composed of an operational amplifier 80, a capacitor C1connected between the inverting (−) input terminal and the outputterminal of the operational amplifier 80, and a resistor R1 connected inseries between the output terminal of the rectifying circuit 5 and theinverting (−) input terminal of the operational amplifier 80. Thenon-inverting (+) input terminal of the operational amplifier 80 isconnected to ground.

Reference numeral 9 denotes a reset circuit, and the reset circuit 9 iscomposed of a transistor having a collector and an emitter connectedbetween both terminals of the capacitor C1. The output signal 73 formthe logic circuit 72 of the delay circuit 7 is inputted to a baseterminal of the transistor of the reset circuit 9. Reference numeral 10is a comparator. An integrated output value Vint, which is an outputsignal from the operational amplifier 80 of the integrating circuit 8,is inputted to the inverting (−) input terminal of the comparator 10.

Reference numeral 40 denotes a reference voltage output circuit,reference numeral 8B denotes an integrating circuit. The integratingcircuit 8B has a similar configuration to that of the integratingcircuit 8, and is composed of an operational amplifier 80B, a capacitorC1B connected between the inverting (−) input terminal and the outputterminal of the operational amplifier 80B, and a resistor R1B connectedin series between the output terminal of the reference voltage outputcircuit 40 and the inverting (−) input terminal of the operationalamplifier 80B. The reference voltage vref from the reference voltageoutput circuit 40 is inputted to the resistor R1B of the integratingcircuit 8B. In addition, reference numeral 9B denotes a reset circuit.The reset circuit 9B has a similar configuration to that of the resetcircuit 9, and is composed of a transistor having a collector and anemitter connected between both terminals of the capacitor C1B. Theoutput signal 73 from the logic circuit 72 of the delay circuit 7 isinputted to a base of the transistor of the reset circuit 9B. Anintegrated output value VintB, which is the output signal from theoperational amplifier 80B of the integrating circuit 8B, is inputted tothe non-inverting (+) input terminal of the comparator 10.

The reference voltage Vref in FIGS. 11 and 12 in the aforementionedprior art device and the reference voltage vref outputted from thereference voltage output circuit 40 in FIG. 1, i.e., a device of thepresent embodiment, have a relation as specified by the followingequation (2):

Vref=vref×Ton/(R1B×C1B)   (2)

Accordingly, the integrated output value VintB, which is obtained byintegrating over time the reference voltage vref in the integratingcircuit 8B, becomes the reference voltage Vref indicated by the equation(2). The integrated output value Vint of the high-frequency componentand the integrated output value VintB of the reference voltage vref arecompared to each other in the comparing circuit 10. In case theintegrated output value Vint is larger than the integrated output valueVintB, the output signal is “0”, and it is judged to be a normalelectrical discharge pulse. In case the integrated output value Vint issmaller than the integrated output value VintB, it is judged to be anabnormal electrical discharge pulse such as an arc electrical dischargepulse.

Feedback control based on the output signals from the comparing circuit10 is described hereunder.

In FIG. 1, reference numeral 110 denotes an abnormal electricaldischarge judging circuit for sensing an abnormal electrical dischargepulse such as an arc electrical discharge pulse, which is caused by adefective machining clearance or the like. If the comparing circuit 10outputs a signal “1” at a predetermined timing and the abnormalelectrical discharge judging circuit 110 judges that it is an abnormalelectrical discharge pulse, the number is counted by the counter CT1implemented in an IC. Reference numeral 120 is a normal electricaldischarge judging circuit for sensing a normal electrical dischargepulse. If the comparing circuit 10 outputs a signal “0” at apredetermined timing and the normal electrical discharge judging circuit120 judges that it is a normal electrical discharge pulse, the number iscounted by the counter CT2 also implemented in an IC.

The counter CT1 outputs a signal if it counts the abnormal electricaldischarge pulses, e.g., up to four, and the signal is inputted to an UPterminal of an up-down counter CT4, which has ten stages from 0 to 9.The counter CT2 outputs a signal if it counts the normal electricaldischarge pulses, e.g., up to eight, and the signal is inputted to aclear signal input terminal and a counter CT3. The counter CT3 outputs asignal if the signals outputted from the counter CT2 reach, e.g., eightor sixteen. This signal is inputted to the UP terminal of the up-downcounter CT4. The signal outputted from the counter CT1 is inputted tothe clear signal input terminal of the counter CT3.

Each of the counters CT1, CT2 and CT3 is constructed such that it clearsits count value when the count number reaches a preset count number.Namely, if the counter CT1 counts abnormal electrical discharge pulsesup to four before the counter CT2 counts normal electrical dischargepulses up to eight, the count number of the up-down counter CT4increases by one, and the count number of the counter CT3 is cleared.Here, unless the counter CT1 counts four during each eight counts of thecounter CT2 while the counter CT2 counts eight times or sixteen times ofthe eight counts, the counter CT3 generates an output, and the countnumber of the up-down counter CT4 decreases by one.

Reference numeral 130 denotes the clear signal input terminal of theup-down counter CT4, DS denotes a digital switch for manually setting adesired count number for the up-down counter CT4 except 0 or 9, Ddenotes a decoder for outputting a signal to one of its output terminals0 to 9, which correspond to the count number of the up-down counter CT4,and reference numeral 140 denotes a machining condition setting unitwhich has ten setting stages from 0 to 9 for a separating distance of areciprocating motion and a cycle of a reciprocating movement (or amachining time in a short distance) . In the machining condition settingunit 140, an Nth stage of machining condition, which is selectedcorresponding to an output from the decoder D, is operated. Then, aterminal 150 a inputs an electrode raising pulse signal, which has apulse width for assuring a predetermined separating distance at a presetfixed cycle, into a servo control unit 150, so that the electrode 2 isactuated under servo-feed control to the workpiece 3.

The operated stage of the machining condition setting unit 140 is notchanged as long as the counter CT1 or the counter CT3 outputs a signalso as to increase or decrease and change the count number of the up-downcounter CT4. Moreover, signals of a preset pulse width are repeatedlyoutputted for the servo control unit 150 to make the operated stagecarry out an opening operation through a predetermined opening distanceat a preset cycle.

With such a structure, if the abnormal electrical discharge judgingcircuit 110 counts four or more abnormal electrical discharge pulsesthrough the counter CT1 during a predetermined time period, i.e., whilethe counter CT2 counts eight normal electrical discharge pulses, themachining condition setting unit 140, which is able to set the openingdistance for the reciprocating motion into two or more steps, masks onecount for the count number of the up-down counter CT4, thereby switchingthe machining condition setting unit 140 such that the opening distanceis made larger or longer.

To the contrary, in case of switching the machining condition settingunit 140 such that the opening distance is made shorter, the machiningcondition setting unit 140 is switched so as to make the openingdistance longer after clearing the counter CT3, namely, after the outputfrom the counter CT1. Thereafter, a down signal is inputted to theup-down counter CT4 so as to operate it to reduce one count from thecount number, unless the abnormal electrical discharge judging circuit110 counts four or more abnormal electrical discharge pulses through thecounter CT1 at any time during a time period longer than thepredetermined time period, namely, while the counter CT3 counts from oneor more times to eight times or to sixteen times of eight counts of thenormal electrical discharge pulses, which are counted by the counterCT2. Thus, there are no abnormal electrical discharge pulses at all, andthe opening distance for the reciprocating movement is changed and keptinto a state such that table machining is possible by the normalelectrical discharge pulses.

As described above, the present embodiment of the electrical dischargestate detecting device for an electrical discharging machine comprises:the high-frequency component detecting means composed of the high-passfilter for detecting a high-frequency component superimposed on eitheran electrical discharge voltage or an electrical discharge current atthe machining clearance between the electrode 2 and the workpiece 3; thefirst integrating means composed of the integrating circuit 8 forintegrating, over time, the magnitude of the high-frequency componentdetected by the high-frequency component detecting means; the referencevoltage output means composed of the reference voltage output circuit 40for outputting the reference voltage vref; the second integrating meanscomposed of the integrating circuit 8B for integrating, over time, themagnitude of the reference voltage vref outputted from the referencevoltage output means; the control means for controlling a starting andan ending of the integrations of the first integrating means and secondintegrating means, including the electrical discharge generationdetecting circuit 6, the logic circuit 62, the delay circuit 7 and thereset circuits 9 and 9B; and the comparing means composed of thecomparator 10 for comparing an integrated value Vint obtained by thefirst integrating means and an integrated value VintB obtained by thesecond integrating means, which are controlled by the controlling means.

Accordingly, the high-pass filter 4 detects the high-frequency componentsuperimposed on either the electrical discharge voltage or theelectrical discharge current at the machining clearance betweenelectrode 2 and the workpiece 3. The magnitude of the high-frequencycomponent is integrated over time by the integrating circuit 8. Inaddition, the magnitude of the reference voltage vref outputted from thereference voltage output circuit 40 is integrated over time by theintegrating circuit 8B. Here, the starting and ending of theintegrations in the integrating circuit 8 and integrating circuit 8B arecontrolled by the electrical discharge generation detecting circuit 6,logic circuit 62, delay circuit 7 and reset circuits 9 and 9B. Theintegrated value Vint obtained by the integrating circuit 8 is comparedwith the integrated value VintB obtained by the integrating circuit 8Bthrough the comparator 10.

In this way, the reference voltage vref is integrated over time by theintegrating circuit 8B, and its integrated value VintB is employed asthe comparison value for judging if the electrical discharge state ofthe electrical discharge machine is a normal electrical discharge pulseor an abnormal electrical discharge pulse such as an arc electricaldischarge pulse, so that precise setting of the reference value can becarried out.

In the electrical discharge state detecting device for an electricaldischarge machine according to the present embodiment, the firstintegrating means, which is composed of the integrating circuit 8, usesa magnitude of a rectified component vrec obtained by rectifying thehigh-frequency component by the rectifying circuit 5 as the magnitude ofthe high-frequency component to be integrated over time.

In this way, it is possible to make the amount of variation of theintegrated value smaller since the magnitude of the rectified componentvrec, obtained by rectifying the high-frequency component, is integratedover time. Therefore, it is possible to correctly judge if it is anormal electrical discharge pulse or an abnormal electrical dischargepulse such as an arc electrical discharge pulse.

Second Embodiment

FIG. 2 is a circuit diagram showing the construction of the electricaldischarge state detecting device for an electrical discharge machineconstructed in accordance with a second embodiment of the presentinvention. Similar structure to that of the previously describedembodiment or corresponding parts are identified by the same referencenumerals and characters to eliminate their detailed description. Thecircuit configuration for feedback control based on the output signalsfrom the comparing circuit 10 is similar to that of the aboveembodiment, and its description will be omitted too.

In FIG. 2, a switch 30 is arranged between the rectifying circuit 5 andthe integrating circuit 8 so as to control the inputting of the outputsignal vrec, which is rectified by the rectifying circuit 5, to theintegrating circuit 8. In addition, a switch 30B is arranged between thereference voltage output circuit 40 and the integrating circuit 8B so asto control the inputting of the reference voltage vref from thereference voltage output circuit 40 to the integrating circuit 8B. Theswitches 30 and 30B have a function to stop the integrating operationsof the integrating circuits 8 and 8B, which function is defined as amask hereinafter. S1 indicates the same as S1 in FIG. 16, namely, asignal for indicating the ON/OFF state of the internal switching elementfor use in controlling the current of the electrical discharge powersource 1. Reference numeral 50 denotes a mask time limit output circuitfor outputting a mask time width m1 at the time of the ON rise of thecurrent control switching element. Reference numeral 50 s denotes itsoutput signal. Reference numeral 51 denotes a mask time limit outputcircuit for outputting a mask time width m2 at the time of OFF fall ofthe current control switching element. Reference numeral 51 s denotesits output signal. Reference numeral 52 denotes a logic circuit whichoutputs the output signal 53 inverted by the logic OR of the outputsignal 50 s obtained from the mask time limit output circuit 50 and theoutput signal 51 s obtained from the mask time limit output circuit 51.Reference numeral 54 denotes a logic circuit which outputs an outputsignal 55 of a logic AND of the output signal 63 obtained from the logiccircuit 62 and the output signal 53 obtained from the logic circuit 52.The output signal 55 obtained from this logic circuit 54 drives theswitches 30 and 30B. When the output signal 55 is at an H level, theswitches 30 and 30B are turned off, and, in turn, when the output signal55 is at an L level, the switches 30, 30B are turned on.

Mask time limit output circuits 50 and 51 shown in FIG. 2 may becomposed of one-shot multivibrators 500 and 510 shown in FIG. 3, forexample.

The one-shot multivibrator 500 outputs a predetermined mask time widthm1, which is set by a circuit constant of a resistor R500 and acapacitor C500, at the time of the ON rise of a signal S1. The one-shotmultivibrator 510 outputs a predetermined mask time width m2, which isset by the circuit constant of a resistor R510 and a capacitor C510, atthe time of the OFF fall of a signal S2.

Next, an operation is described referring to FIG. 4.

FIG. 4 is a timing chart showing input/output signal waveforms at mainparts in FIG. 2.

The same parts as those in FIG. 17, which indicates the input/outputsignal waveforms of the prior art device, or corresponding parts areidentified by the same reference numerals and characters to omit theirdescription.

Reference character A in FIG. 4 denotes an electrical discharge voltagewaveform. B in FIG. 4 denotes an output signal waveform of the high-passfilter 4. I in FIG. 4 denotes the output signal waveform of the logiccircuit 72. S1 in FIG. 4 denotes the output signal waveform of theinternals witching element for use in controlling the electricaldischarge current in the machining power source 1. M1 in FIG. 4 denotesan output signal waveform of the mask time limit output circuit 50,which outputs a mask signal having the mask time width m1 at the time ofthe ON rise of the internal switching element for use in controlling theelectrical discharge current. M2 in FIG. 4 denotes an output signalwaveform of the mask time limit output circuit 51. The mask time limitoutput circuit 51 outputs the mask signal having the time limit width m2at the time of the OFF fall of the internal switching element for use incontrolling the current of the machining power source 1. The mask timewidth m1 is set to a larger value than the time width b1 of the spikevoltage 24, and the mask time width m2 is set to a larger value than thetime width b2 of the spike voltage 24. Reference character F in FIG. 4denotes the output waveform obtained by integrating, over time, theoutput signal vrec from the rectifying circuit 5 through the integratingcircuit 8. Reference character G in FIG. 4 denotes an output waveformobtained by integrating, over time, the reference signal vref from thereference voltage output circuit 40 by the integrating circuit 8.Integrating operations of the integrating circuits 8 and 8B are stoppedduring the mask time widths m1 and m2 and the integrated waveform keepsits value during these time widths.

As apparent from F in FIG. 4, influence of the spike voltage 24 iscompletely eliminated and there is no erroneous detection as shown byVint2 in F in FIG. 17. The integrating operation for the referencevoltage is also stopped during the integrating operation for therectified output is stopped, and there is no error in deciding if it isa normal electrical discharge pulse or an abnormal electrical dischargepulse such as an arc electrical discharge pulse at the stage of judgmentby the comparator 10.

The present embodiment of the electrical discharge state detectingdevice for an electrical discharge machine thus comprises: thehigh-frequency component detecting means including the high-pass filter4 for detecting a high-frequency component superimposed on either anelectrical discharge voltage or an electrical discharge current at themachining clearance between the electrode 2 and the workpiece 3; therectifying means including the rectifying circuit 5 for outputting therectifying component vrec obtained by rectifying the high-frequencycomponent detected by the high-frequency component detecting means; thefirst integrating means including the integrating circuit 8 forintegrating, over time, the magnitude of the rectified component vrecoutputted from the rectifying means; the reference voltage output meansincluding the reference voltage output circuit 40 for outputting thereference voltage vref; the second integrating means including theintegrating circuit 8B for integrating, over time, the magnitude of thereference voltage vref outputted from the reference voltage outputmeans; the integration stopping means, including the mask time limitoutput circuits 50 and 51, logic circuits 52 and 54 and switches 30 and30B, for stopping the integrations in the first integrating means andsecond integrating means only for the predetermined times m1 and m2 onthe basis of the ON time and OFF time of the internal switching elementfor use in controlling current in the machining power source 1; thecontrol means, including the electrical discharge generation detectingcircuit 6, logic circuit 62, delay circuit 7 and reset circuits 9 and9B, for controlling a starting and an ending of the integrations in thefirst integrating means and second integrating means; and the comparingmeans including the comparator 10 for comparing the integrated valueVint obtained by the first integrating means and the integrated valueVintB obtained by the second integrating means, which are controlled bythe controlling means.

Accordingly, the high-pass filter 4 detects the high-frequency componentsuperimposed on either the electrical discharge voltage or theelectrical discharge current at the machining clearance between theelectrode 2 and the workpiece 3. The high-frequency component isrectified by the rectifying circuit 5, and the magnitude of theoutputted rectified component vrec is integrated, over time, by theintegrating circuit 8. The magnitude of the reference voltage vrefoutputted from the reference voltage output circuit 40 is integrated,over time, by the integrating circuit 8B. Utilizing the mask time limitoutput circuits 50 and 51, and the logic circuits 52 and 54 and switches30 and 30B, the integrations in the integrating circuit 8 andintegrating circuit 8B are stopped only for the predetermined times m1and m2 on the basis of the operations at the ON time and OFF time of theinternal switching element for use in controlling current in themachining power source 1. The starting and ending of the integrations inthe integrating circuit 8 and integrating circuit 8B are controlled bythe electrical discharge generation detecting circuit 6, logic circuit62, delay circuit 7 and reset circuits 9 and 9B. The integrated valueVint obtained by the integrating circuit 8 and the integrated valueVintB obtained by the integrating circuit 8B are compared to each otherwith the comparator 10.

Accordingly, the integrating operation is stopped only for thepredetermined times m1 and m2 synchronously with the operation of theinternal switching element for use in controlling current in themachining power source 1, so that the influence of disturbances can beeliminated and accurate detecting of the electrical discharge state canbe attained.

Third Embodiment

FIG. 5 is a circuit diagram showing the construction of the electricaldischarge state detecting device for an electrical discharge machineconstructed in accordance with a third embodiment of the presentinvention. The construction similar to that of the previouslyembodiments or corresponding portions are identified with the samereference numerals and characters, thereby omitting their detaileddescription.

The circuit configuration for feedback control based on the outputsignals from the comparing circuit 10 is similar to that of the aboveembodiment, and hence a further description will be omitted.

In FIG. 5, reference numeral 35 denotes a difference circuit foroutputting an output signal 37, which is a difference component betweenthe output signal vrec from the rectifying circuit 5 and the referencevoltage vref from the reference voltage output circuit 40. The outputsignal 37 from the difference circuit 35 is cut off from the integratingcircuit 8 after the switch 30 is operated only for the mask time widthsm1 and m2 as in the second embodiment, thereby to cause the integratingoperation in the integrating circuit 8 to be stopped.

In this case, in the second embodiment, the value Vint, which isobtained by integrating, over time, the output signal vrec from therectifying circuit 5, and the value VintB, which is obtained byintegrating, over time, the reference voltage vref from the referencevoltage output circuit 40, are compared to each other by the comparator10. Then, it is judged if the discharge pulse is a normal electricaldischarge pulse or an abnormal electrical discharge pulse such as an arcelectrical discharge pulse. Thus, it is necessary to provide theswitches 30 and 30B, integrating circuits 8 and 8B and reset circuits 9and 9B, i.e., two of each type of switch. To the contrary, in thepresent embodiment, the difference between the output signal vrec fromthe rectifying circuit 5 and the reference voltage vref from thereference voltage output circuit 40 is integrated, over time, and,lastly, it is compared with a value 0 by the comparator 10. Then, it isjudged if it is a normal electrical discharge pulse or an abnormalelectrical discharge pulse such as an arc electrical discharge pulse.That is, in the present embodiment, it is possible to accomplish thejudgment similar to that of the second preferred embodiment using onlyone switch 30, one integrating circuit 8 and one reset circuit 9.

As described above, the present embodiment of the electrical dischargestate detecting device for an electrical discharge machine comprises:the high-frequency component detecting means including the high-passfilter 4 for detecting the high-frequency component superimposed oneither an electrical discharge voltage or an electrical dischargecurrent at the machining clearance between the electrode 2 and theworkpiece 3; the rectifying means including the rectifying circuit 5 foroutputting the rectified component vrec obtained by rectifying thehigh-frequency component detected by the high-frequency componentdetecting means; the reference voltage output means including thereference voltage output circuit 40 for outputting the reference voltagevref; the difference output means including the difference circuit 35for outputting a difference between the rectified component vrecoutputted from the rectifying means and the reference voltage vrefoutputted from the reference voltage output means; the integrating meansincluding the integrating circuit 8 for integrating the differenceoutputted from the difference output means; the integration stoppingmeans, including the mask time limit output circuits 50 and 51, logiccircuits 52 and 54 and switch 30, for stopping integration in theintegrating means only for the predetermined times m1 and m2 on thebasis of the ON time and OFF time of the internal switching element foruse in controlling current in the machining power source 1; the controlmeans, including the electrical discharge generation detecting circuit6, logic circuit 62, delay circuit 7 and reset circuit 9, forcontrolling starting and ending of the integrating means; and thecomparing means including the comparator 10 for comparing the integratedvalue Vint obtained by said integrating means and the reference value 0,which are controlled by the controlling means.

The high-pass filter 4 detects the high-frequency component superimposedon either the electrical discharge voltage or the electrical dischargecurrent at the machining clearance between the electrode 2 and theworkpiece. The high-frequency component is rectified by the rectifyingcircuit 5, and the difference between the outputted rectified componentvrec and the reference voltage vref outputted from the reference voltageoutput circuit 40 is integrated over time by the integrating circuit 8.The mask time limit output circuits 50 and 51, logic circuits 52 and 54and switch 30 operate to stop the integration in the integrating circuit8 only for the predetermined times m1 and m2 on the basis of the ON timeand OFF time of the internal switching element for use in controllingcurrent of the machining power source 1. Here, the starting and endingof the integration in the integrating circuit 8 are controlled by theelectrical discharge generation detecting circuit 6, logic circuit 62,delay circuit 7 and reset circuit 9. Then, the integrated value Vintobtained by the integrating circuit 8 and the reference value 0 arecompared by the comparator 10.

Consequently, the difference between the rectified component vrec of thehigh-frequency component and the reference voltage vref is integratedover time, so that the number of the integrating circuit 8 and theswitches 30 for stopping the integration only for the predeterminedtimes m1 and m2 is reduced and the circuit configuration can besimplified.

Fourth Embodiment

FIG. 6 is a circuit diagram showing a configuration of the electricaldischarge state detecting device for an electrical discharge machine inaccordance with a fourth embodiment of the present invention. In FIG. 6,a mask time limit changing circuit 56 is added to the second embodimentof FIG. 2. The same configuration as that of the aforesaid embodiment orcorresponding portions are identified by the same reference charactersand numerals, thereby omitting their detailed description.

The circuit configuration for feedback control based on the outputsignals from the comparing circuit 10 is similar to that of the aboveembodiment, and thus a further description will be omitted.

In FIG. 6, it is known that the time widths b1 and b2 of the spikevoltage 24 indicated by the character B in FIG. 4 depend on themachining current value. The mask time limit changing circuit 56 havingthe machining current value read therein outputs the output signals 57and 58. Each of these output signals 57 and 58 is inputted to each ofthe mask time limit output circuits 50 and 51. For example, when themachining current value is high, the mask time width m1 of the mask timelimit output circuit 50 is increased based on the output signal 57 fromthe mask time limit changing circuit 56. In turn, when the machiningcurrent value is low, the mask time width m2 of the mask time limitoutput circuit 51 is reduced based on the output signal 58 from the masktime limit changing circuit 56.

The mask time limit changing circuit 56 and the mask time limit outputcircuits 50 and 51 are described referring to FIGS. 7 and 8. FIG. 7 is adata table showing a machining current value, which is obtained by themask time limit output circuit, and a time width changing signalcorresponding to the mask time width. FIG. 8 is a circuit diagramshowing a configuration of the mask time limit output circuit.

The mask time limit changing circuit 56 outputs time width changingsignals a1 and a2, as output signals 57 and 58 shown in FIG. 6, inaccordance with the mask time widths m1 and m2 corresponding to themachining current value at that time, while using the data table shownin FIG. 7. For example, the time width changing signal a1 is outputtedcorresponding to a machining current value of 1 to 20 Ampere (A), andthe time width changing signal a2 is outputted corresponding to amachining current value of 21 to 80 (A).

These time changing signals a1 and a2 are outputted to the mask timelimit output circuit 50, as shown in FIG. 8. The mask time limit outputcircuit 50 is composed of one-shot multivibrators 500 and 501, and themask time limit output circuit 51 is composed of one-shot multivibrators510 and 511. The one-shot multivibrator 500 sets the mask time width m1,which is a circuit constant determined by a resistor R500 and acapacitor C500 (e.g., 2 μs) , and outputs the mask time width of 2 μs atthe time of ON rise of the signal S1. The one-shot multivibrator 501sets the mask time width m1, which is a circuit constant determined by aresistor R501 and a capacitor C501 (e.g., at 8 μs), and outputs the masktime width of 8 μs at the time of ON rise of the signal S1. The one-shotmultivibrator 510 sets the mask time width m2, which is a circuitconstant determined by a resistor R510 and a capacitor C510 (e.g., 4μs), and outputs the mask time width of 4 μs at the time of OFF fall ofthe signal S1. The one-shot multivibrator 511 sets the mask time widthm2, which is a circuit constant determined by a resistor R511 and acapacitor C511 (e.g., 10 μs), and outputs the mask time width of 10 μsat the time of the OFF fall of the signal S1.

As described above, the present embodiment of the electrical dischargestate detecting device for an electrical discharge machine comprises:the high-frequency component detecting means including the high-passfilter 4 for detecting the high-frequency component superimposed oneither an electrical discharge voltage or an electrical dischargecurrent at the machining clearance between the electrode 2 and theworkpiece 3; the rectifying means including the rectifying circuit 5 foroutputting the rectified component vrec obtained by rectifying thehigh-frequency component detected by the high-frequency componentdetecting means; the first integrating means including the integratingcircuit 8 for integrating, over time, the magnitude of the rectifiedcomponent vrec outputted from the rectifying means; the referencevoltage outputting means including the reference voltage output circuit40 for outputting the reference voltage vref; the second integratingmeans including the integrating circuit 8B for integrating, over time,the magnitude of the reference voltage vref outputted from the referencevoltage output means; the integration stopping means, including the masktime limit output circuits 50 and 51, logic circuits 52 and 54 andswitches 30 and 30B, for stopping integration in the first integratingmeans and second integrating means only for the predetermined times m1and m2 on the basis of the ON time and OFF time of the internalswitching element for use in controlling current in the machining powersource 1; the time changing means including the mask time limit changingcircuit 56 for changing the durations of the predetermined times m1 andm2, during which the integration is stopped by the integration stoppingmeans, in accordance with a magnitude of the machining current value;the control means, including the electrical discharge generationdetecting circuit 6, logic circuit 62, delay circuit 7 and resetcircuits 9 and 9B, for controlling starting and ending of theintegrations by the first integrating means and second integratingmeans; and the comparing means including the comparator 10 for comparingthe integrated value Vint obtained by the first integrating means andthe integrated value VintB obtained by the second integrating means,which are controlled by the controlling means.

Accordingly, the high-pass filter 4 detects the high-frequency componentsuperimposed on either the electrical discharge voltage or theelectrical discharge current at the machining clearance between theelectrode 2 and the workpiece 3. The high-frequency component isrectified by the rectifying circuit 5, and the magnitude of theoutputted rectified value vrec is integrated over time by theintegrating circuit 8. In addition, the magnitude of the referencevoltage vref outputted from the reference voltage output circuit 40 isintegrated over time by the integrating circuit 8B. Utilizing the masktime limit output circuits 50 and 51, logic circuits 52 and 54 andswitches 30 and 30B, integrations in the integrating circuit 8 and theintegrating circuit 8B are stopped only for the predetermined times m1and m2 on the basis of the ON time and OFF time of the internalswitching element for use in controlling current in the machining powersource 1. In the mask time limit changing circuit 56, the durations ofthe predetermined times m1 and m2, during which the integrations arestopped by the mask time limit output circuits 50 and 51, logic circuits52 and 54 and switches 30 and 30B, are changed in accordance with themagnitude of the machining current value. Here, starting and ending ofthe integrations by the integrating circuit 8 and integrating circuit 8Bare controlled by the electrical discharge generation detecting circuit6, logic circuit 62, delay circuit 7 and reset circuits 9 and 9B. Then,the integrated value Vint obtained by the integrating circuit 8 iscompared with the integrated value VintB obtained by the integratingcircuit 8B by the comparator 10.

Consequently, the durations of the predetermined times m1 and m2 of themask time limit are changed in accordance with a magnitude of themachining current, so that influence of disturbances can be surelyeliminated and accurate detecting of the electrical discharge state canbe attained.

Fifth Embodiment

FIG. 9 is a circuit diagram showing the configuration of the electricaldischarge state detecting device for an electrical discharge machine inaccordance with a fifth embodiment of the present invention. FIG. 10 isa timing chart showing input/output signal waveforms at main parts inFIG. 9. The same configurations as those of the previously describedembodiments or corresponding portions are identified by the samereference numerals and characters, and their further detaileddescription is omitted. The circuit configuration for feedback controlbased on the output signals from the comparing circuit 10 is similar tothat of the above-described embodiment, and its further description toowill be omitted.

In the prior art device, in case the electrical discharge pulse widthTon in the electrical discharge voltage waveform at the machiningclearance between the electrode 2 and the workpiece 3 is small, asindicated by A in FIG. 10, the integration period per electricaldischarge pulse is short, so that the integrated output of thehigh-frequency component becomes so low that sufficiently accuratedetecting of the high-frequency component becomes difficult.

Reference numeral 30 denotes a switch for separating the rectifyingcircuit 5 from the integrating circuit 8. Reference number 30B denotes aswitch for separating the reference voltage output circuit 40 from theintegrating circuit 8B. Reference numeral 75 denotes a counter forcounting the number of pulses in reference character I in FIG. 10, whichis an output signal waveform of the output signal 73 from the logiccircuit 72. The output signal from the counter 75 is inputted to thereset circuit 9. Then, for example, as shown by the output signal 76from the counter 75 in FIG. 10, if the number of counted pulses of theoutput signal 73 from the logic circuit 72 reaches four, the outputsignal 76 becomes in H level. During the output signal 73 from the logiccircuit 72 is at the H level, the switches 30 and 30B are turned off,and the integrating circuits 8 and 8B are separated from the rectifyingcircuit 5 and the reference voltage output circuit 40, so that theintegrating operations of the integrating circuits 8 and 8B are stopped,thereby holding the integrated output value. When the counter 75 countsthe output signals 73 from the logic circuits 72 corresponding to fourelectrical discharge pulses, the output signal 76 from the counter 75becomes the H level. Then, the reset circuits 9 and 9B reset theintegrated output value of the integrating circuits 8 and 8B. That is,in FIGS. 9 and 10, the high-frequency components corresponding to fourelectrical discharge pulses are integrated over time, and the comparator10 compares the integrated output Vint with the integrated output VintB,which is obtained by integrating, over time, the reference voltage vreffrom the reference voltage output circuit 40 by the integrating circuit8B only for the same period, at the time of completion of the fourthelectrical discharge pulse. According to such a configuration, it issatisfactory that the switch 30, counter 75 and integrating circuit 8Bbe added to the prior art device shown in FIG. 11.

As described above, the present embodiment of the electrical dischargestate detecting device for an electrical discharge machine comprises:the high-frequency component detecting means including the high-passfilter 4 for detecting the high-frequency component superimposed oneither the electrical discharge voltage or the electrical dischargecurrent at the machining clearance between the electrode 2 and theworkpiece 3; the rectifying means including the rectifying circuit 5 foroutputting the rectified component vrec obtained by rectifying thehigh-frequency component detected by the high-frequency componentdetecting means; the count means including the counter 75 for counting aplurality of continual electrical discharge pulses; the firstintegrating means including the integrating circuit 8 for integrating,over time, the magnitude of the rectified component vrec outputted fromthe rectifying means and adding them only for the number of electricaldischarge pulses counted by the count means; the reference voltageoutput means including the reference voltage output circuit 40 foroutputting the reference voltage vref; the second integrating meansincluding the integrating circuit 8B for integrating, over time, themagnitude of the reference voltage vref outputted from the referencevoltage output means and adding them only for the number of electricaldischarge pulses counted by the count means; the control means,including the electrical discharge generation state detecting circuit 6,logic circuit 62, delay circuit 7 and reset circuits 9 and 9B, forcontrolling a starting and an ending of integrations in the firstintegrating means and second integrating means; and the comparing meansincluding the comparator 10 for comparing the integrated value Vintobtained by the first integrating means and the integrated value VintBobtained by the second integrating means, which are controlled by thecontrolling means.

Accordingly, the high-pass filter 4 detects the high-frequency componentsuperimposed on the electrical discharge voltage or the electricaldischarge current at the machining clearance between the electrode 2 andthe workpiece 3. The high-frequency component is rectified by therectifying circuit 5, and the magnitude of the outputted rectifyingcomponent vrec is integrated over time by the integrating circuit 8 andadded only for a plurality of continual discharge pulses counted by thecounter 75. Then, the magnitude of the reference voltage vref outputtedfrom the reference voltage output circuit 40 is integrated over time bythe integrating circuit 8B and added only for a plurality of continualdischarge pulses counted by the counter 75. Here, the starting andending of the integrations in the integrating circuit 8 and integratingcircuit 8B are controlled by the electrical discharge generationdetecting circuit 6, logic circuit 62, delay circuit 7 and resetcircuits 9 and 9B. Then, the integrated value Vint obtained by theintegrating circuit 8 is compared with the integrated value VintBobtained by the integrating circuit 8B by the comparator 10.

Consequently, the high-frequency component for a plurality of continualelectrical discharge pulses is integrated over time, so that anelectrical discharge state can be sensed accurately even when theelectrical discharge pulse width Ton is small.

While the high-frequency component detecting means of each of theaforesaid embodiments uses the high-pass filter, the present inventionis not limited to this in practice, and any device may be used as longas it detects the high-frequency component of the electrical dischargevoltage or the electrical discharge current at the machining clearancebetween the electrode and the workpiece. For example, a similar effectcan be attained in case of using a bandpass filter having high-passfiltering characteristic for detecting the high-frequency component andcutting off a region of a frequency higher than that.

While detecting of the high-frequency component of the electricaldischarge voltage waveform has been described in each of the aforesaidembodiments, it is apparent that the present invention can be applied toa high-frequency component of an electrical discharge current waveformor an impedance waveform at the machining clearance.

It is also apparent that, while the preferred embodiment is describedwith reference to a hardware implementation, it can implemented as wellin a software configuration.

In addition, while each of the aforesaid preferred embodiments isrealized in a shape-forming electrical discharge machine, the presentinvention is not limited to this in practice, and it is apparent, forinstance, that the present invention can be applied also to a wirecutting electrical discharge machine.

As described above, according to the electrical discharge statedetecting device for an electrical discharge machine of the firstembodiment, the high-frequency component, which is superimposed oneither the electrical discharge voltage or the electrical dischargecurrent at the working clearance between the electrode and theworkpiece, is detected by the high-frequency component detecting means.The magnitude of the high-frequency component is subjected totime-integration in the first integrating means. In addition, themagnitude of the reference voltage outputted from the reference voltageoutput means is subjected to time-integration in the second integratingmeans. Here, the starting and ending of the integrations in the firstintegrating means and second integrating means are controlled by thecontrolling means. Then, the integrated value obtained by the firstintegrating means is compared with the integrated value obtained by thesecond integrating means through the comparing means. In this way, thereference voltage is integrated by the second integrating means, and theintegrated value is employed as the comparison value for judging whetheror not the electrical discharge state of the electrical dischargemachine is a normal electrical discharge pulse or an abnormal electricaldischarge pulse such as an arc electrical discharge pulse. Thus, it ispossible to carry out precise setting of the reference value.

The magnitude of the high-frequency component, which is subjected totime-integration in the first integrating means is the magnitude of therectified component obtained by rectifying the high-frequency component.Thus, it is possible to make the amount of variation of the integratedvalue smaller since the magnitude of the rectified component, obtainedby rectifying the high-frequency component, is integrated over time.Therefore, it is possible to correctly judge if it is a normalelectrical discharge pulse or an abnormal electrical discharge pulsesuch as an arc electrical discharge pulse.

According to the electrical discharge state detecting device for anelectrical discharge machine of the second embodiment, thehigh-frequency component, which is superimposed on either the electricaldischarge voltage or the electrical discharge current at the workingclearance between the electrode and the workpiece, is detected by thehigh-frequency component detecting means. The high-frequency componentis rectified by the rectifying means, and the magnitude of the outputtedrectified component is integrated over time by the first integratingmeans. In addition, the magnitude of the reference voltage outputtedfrom the reference voltage output means is integrated over time by thesecond integrating means. The integrations in the first integratingmeans and second integrating means are stopped by the integrationstopping means only for a predetermined period of time on the basis ofan operation of the internal switching element for use in controllingcurrent in the machining power source. The predetermined period of timeis set to the time duration of the spike voltage generated at this time,and error factors of the integrated value are eliminated by stoppingintegration as above. Here, the starting and ending of the firstintegrating means and second integrating means are controlled by thecontrol means. Then, the integrated value from the first integratingmeans is compared with the integrated value from the second integratingmeans through the comparing means. In this way, the integratingoperation is stopped only for a predetermined period of time synchronouswith the operation of the internal switching element for use incontrolling current in the machining power source, so that it ispossible to eliminate influence of disturbances and to perform accuratedetection of the electrical discharge state.

According to the electrical discharge state detecting device for anelectrical discharge machine of the third embodiment, the high-frequencycomponent, which is superimposed on either the electrical dischargevoltage or the electrical discharge current at the machining clearancebetween the electrode and the workpiece, is detected by thehigh-frequency component detecting means. The high-frequency componentis rectified by the rectifying means, and the difference between theoutputted rectified component and the reference voltage outputted fromthe reference voltage outputting means is outputted from the differencevoltage outputting means and is integrated over time by the integratingmeans. The integration in the integrating means is stopped by theintegration stopping means only for a predetermined period of time onthe basis of an operation of the internal switching element for use incontrolling current in the machining power source. The predeterminedperiod of time is set to a time duration of the spike voltage generatedat this time, and error factors of the integrated value are eliminatedby stopping the integration as above. Here, the starting and stopping ofthe integrating means are controlled by the control means. Then, theintegrated value of the integrating means is compared with the referencevalue 0 through the comparing means. In this way, the difference betweenthe rectified component of the high-frequency component and thereference voltage is integrated over time and compared with thereference value, so that it is possible to reduce the number of theintegrating means and the integration stopping means for stopping theintegration only for a predetermined period of time, thereby simplifyinga circuit configuration.

According to the electrical discharge state detecting device for anelectrical discharge machine of the fourth embodiment, thehigh-frequency component, which is superimposed on either the electricaldischarge voltage or the electrical discharge current at the machiningclearance between the electrode and the workpiece, is detected at thehigh-frequency component detecting means. The high-frequency componentis rectified by the rectifying means, and the magnitude of the outputtedrectified component is integrated over time by the first integratingmeans. The magnitude of the reference voltage outputted from thereference voltage output means is integrated over time by the secondintegrating means. The integrations in the first integrating means andsecond integrating means are stopped by the integration stopping meansonly for a predetermined period of time on the basis of an operation ofthe internal switching element for use in controlling current in themachining power source. The duration of the predetermined period oftime, for which the integrations are stopped by the integration stoppingmeans, is changed by the time changing means in accordance with amagnitude of the machining current value. The predetermined period oftime is properly set to a time duration of the spike voltage generatedin accordance with a magnitude of the machining current value, and errorfactors in the integrated value are eliminated by stopping theintegrations as above. Here, the starting and stopping of the firstintegrating means and second integrating means are controlled by thecontrol means. Then, the integrated value from the first integratingmeans is compared with the integrated value from the second integratingmeans through the comparing means. In this way, a mask time limit ischanged in accordance with the value of the machining current, so thatit is possible to surely eliminate influence of disturbances and performaccurate detection of the electrical discharge state.

According to the electrical discharge state detecting device for anelectrical discharge machine of the fifth embodiment, the high-frequencycomponent, which is superimposed on either the electrical dischargevoltage or the electrical discharge current at the machining clearancebetween the electrode and the workpiece, is detected by thehigh-frequency component detecting means. The high-frequency componentis rectified by the rectifying means. The magnitude of the outputtedrectified component is integrated over time by the first integratingmeans and added only for the number of continual electrical dischargepulses counted by the count means. In addition, the magnitude of thereference voltage outputted from the reference voltage output means isintegrated over time by the second integrating means and added only forthe number of continual electrical discharge pulses counted by the countmeans. Here, the starting and ending of the integrations in the firstintegrating means and second integrating means are controlled by thecontrol means. Then, the integrated value obtained by the firstintegrating means is compared with the integrated value obtained by thesecond integrating means through the comparing means. In this way, thehigh-frequency component are integrated over time for the continualelectrical discharge pulses, so that it is possible to perform anaccurate detection of the electrical discharge state even if theelectrical discharge pulse width is narrow.

What is claimed is:
 1. An electrical discharge state detecting devicefor an electrical discharge machine, comprising: high-frequencycomponent detecting means for detecting a high-frequency componentsuperimposed on either an electrical discharge voltage or an electricaldischarge current at a machining clearance between an electrode and aworkpiece; rectifying means for outputting a rectified componentobtained by rectifying said high-frequency component detected by saidhigh-frequency component detecting means; reference voltage output meansfor outputting a reference voltage; difference output means foroutputting a difference between said rectified component outputted fromsaid rectifying means and said reference voltage outputted from saidreference voltage outputting means; integrating means for integrating,over time, said difference outputted from said difference output means;integration stopping means for stopping an integration in saidintegrating means only for a predetermined time on the basis of anoperation of an internal switching element for use in currentcontrolling of a machining power source; control means for controlling astarting and an ending of the integration in said first integratingmeans; and comparing means for comparing an integrated value obtained bysaid integrating means, which is controlled by said controlling means,with a predetermined reference value.
 2. An electrical discharge statedetecting device for an electrical discharge machine operating on aworkpiece, said detecting device comprising: an electrode disposed abovethe workpiece to detect an electrical discharge from the workpiece; ahigh pass filter connected to said electrode to pass a high frequencycomponent of the electrical discharge; a rectifying circuit receivingthe high frequency component and outputting a rectified signal; areference voltage source for supplying a first reference voltage; asubtractor receiving said reference voltage and said rectified signaland outputting a difference signal; a first integrator receiving thediffernece signal and outputting a signal representing an integration ofthe difference signal over time; a comparator receiving said signalrepresenting the integration of the difference signal over time and asecond reference voltage to determine a state of the discharge of theelectrical characteristic.